The way it handles processes, how much of a toll it takes on the processor, etc, etc, can be changed, thus making battery life better. Also, how noticeable it is, if anything was changed to effect battery life at all, depends on your device and how you use it and if you pay attention to battery life.
After the update my iPhone 5's battery life has been stellar, only gone down 6% since updating over 2 hours ago and using it a lot, usually it would go down like 15% in that period and it has been running just smoother